The use of wireless communication systems is growing with users now numbering well into the millions. One of the popular wireless communications systems is the cellular telephone, having a mobile station (or handset) and a base station. Cellular telephones allow a user to talk over the telephone without having to remain in a fixed location. This allows users to, for example, move freely about the community while talking on the phone.
Cellular telephones may operate under a variety of standards including the code division multiple access (CDMA) cellular telephone communication system as described in TIA/EIA, IS-95, Mobile station-Base Station Compatibility Standard for Dual-Mode Wideband Spread Spectrum Cellular System, published July 1993. CDMA is a technique for spread-spectrum multiple-access digital communications that creates channels through the use of unique code sequences. In CDMA systems, signals can be and are received in the presence of high levels of interference. The practical limit of signal reception depends on the channel conditions, but CDMA reception in the system described in the aforementioned IS-95 Standard can take place in the presence of interference that is 18 dB larger than the signal for a static channel. Typically the system operates with a lower level of interference and dynamic channel conditions.
A CDMA base station communicates with a mobile station with a signal having a basic data rate of 9600 bits/s. The signal is then spread to a transmitted bit rate, or chip rate, of 1.2288 MHz. Spreading applies digital codes to the data bits, which increase the data rate while adding redundancy to the CDMA system. The chips of all the users in that cell are then added to form a composite digital signal. The composite digital signal is then transmitted using a form of quadrature phase shift keying (QPSK) modulation that has been filtered to limit the bandwidth of the signal.
In a code division multiple access (CDMA) spread spectrum communication system, a common frequency band is used for communication with all base stations within that system. If two or more mobile users simultaneously contend for an idle packet-data channel in a system using IS-707, the system will only allow one access to the channel must repeat the transmission of the data packet until it is accepted by the system. The system users transmitting data packets to mobile users also contend for the downlink by being placed in a queue.
Under the current IS-707 standard, when a system user is unable to access the channel, the system user reattempts connection after a predetermined wait. The length of the wait is defined by the IS-707 standard, and is the same for each system user. After each subsequent unsuccessful attempt to connect to the system, the length of the wait is increased until a maximum value is reached. However, if the system users were denied access to an idle channel because multiple users attempted to simultaneously access the channel, each user will attempt to re-access the channel at the same time, causing further collisions.
What is needed is a system that allows the system users to wait for a free channel to connect to the system while reducing the probability of reconnection collision with other system users.